The present invention relates generally to medical equipment and, more particularly, to a high frequency oscillating ventilator for producing positive and negative pressure waves in respiratory air that is supplied to a patient. Advantageously, the high frequency oscillating ventilator (HFOV) of the present invention is specifically configured to operate at reduced noise levels and under reduced power as compared to HFOV's of the prior art.
As opposed to conventional ventilators which ventilate only during the inhalation phase and which rely on human physiological response for ventilation during the expiration phase, HFOV's produce an active exhalation which is critical in the respiration of certain types of patients such as in neonates and/or other child or adult patients suffering from certain lung diseases. In some cases, the lungs of the patient may be incapable of providing adequate ventilation or gas exchange, particularly in the exhalation phase.
In this regard, HFOV's are specifically developed to provide sufficient gas exchange and full oxygenation of a patient whose respiratory abilities in the exhalation phase are compromised. Despite their advantages, HFOV's of the prior art suffer from several deficiencies that detract from their overall utility. For example, one of the more popular HFOV's is constructed similar to that shown and described in U.S. Pat. No. 4,719,910 issued to Jensen and entitled OSCILLATING VENTILATOR AND METHOD (the “Jensen reference”), the entire contents of which is expressly incorporated by reference herein.
The HFOV of the Jensen reference comprises a housing having a magnet and a diaphragm disposed therewithin. A coil is mounted on the first side of the diaphragm and is operative to reciprocate a piston on the first side. The HFOV includes the appropriate circuitry to reverse current polarity in the coil in order to effectuate reciprocation of the piston which, in turn, causes the diaphragm to move back and forth within the housing. The vibrating diaphragm creates positive and negative pressure waves in gas which is supplied to the patient's airway.
Although the HFOV as disclosed in the Jensen reference is effective in producing gas exchange in ventilation of a patient without damaging the patients lungs such by over-pressurization, this HFOV unfortunately produces relatively high noise levels which are undesirable in sensitive environments wherein HFOV's are typically used such as neonatal intensive care units. Furthermore, the HFOV of the Jensen reference relies on an arrangement of spider springs to suspend a linear actuator portion of the coil. Unfortunately, a relatively large amount of power is required to overcome the significant spring forces when reciprocating the linear actuator relative to the coil to cause the diaphragm to vibrate.
Furthermore, the above-described HFOV relies on a dedicated source of gas to cool the coil as well as provide respiratory gasses for the patient. In addition, a fan may be incorporated into the HFOV in order to create sufficient flow of the cooling gasses through the coil. In this regard, a further deficiency associated with this HFOV is excess heating of the coil which degrades the accuracy with which the piston is centered due to resistance changes in the coil as the coil heats up.
High noise levels produced by prior art HFOV's noise may be generated by several sources including noise produced by the fan as well as noise produced by the flow of cooling air traveling through various passageways formed in the coil. Because such cooling gas exit the coil and enter the surrounding environment, additional noise is produced by the out rush of cooling gas through apertures in the coil housing.
A further significant source of noise that may be disruptive to patients as well as to hospital personnel is noise that is generated by the diaphragm. More specifically, in the prior art HFOV described above, the diaphragm includes a relief provided around a circumferential peripheral edge thereof. The relief allows the piston to reciprocate in unison with the diaphragm in order to produce the positive and negative pressure waves in the patient airway. Unfortunately, the consistent back and forth motion of the diaphragm causes the relief to constantly invert in rapid succession creating a snapping noise as the reciprocations occur.
A further source of noise is generated by the piston as it contactor strikes an underside the diaphragm in a repetitive manner during each positive stroke. The constant repetitive striking of the bottom of the diaphragm generates the repetitive slapping noise which only adds to the overall noise produces by the HFOV and which unfortunately disrupts the patient's sleep and recovery. For example, HFOV's of the type described above may produce noise levels of up to 65 dB when operating at full power.
As can be seen, there exists a need in the art for an HFOV that is specifically configured to operate effectively but with reduced sound output in order to avoid disturbing the sleep and rest of patients dependent thereupon. Furthermore, there exists a need in the art for an HFOV that operates at reduced power and which is more energy-efficient than current HFOV's but which matches the clinical performance of existing HFOV's. Additionally, there exists a need in the art for an HFOV that is of reduced size for increased portability in order that the HFOV may be utilized while transporting critically ill patients. Finally, there exists a need in the art for an HFOV that is of simple construction and low cost.